Cross-sectional evidences suggest a relationship between early childhood sleep and cognitive as well as socio-emotional functions. However, the casual relation has not been fully revealed. The current study aims to perform a randomized lab-based crossover nap restriction study on preschoolers, to determine the effects of sleep restriction on preschoolers empathy, prosocial behaviors as well as executive functions.

The study will enroll preschoolers with regular nap habits. Under a randomized repeated-measures crossover design, they follow a strict sleep schedule (≥ 12.5 hours' time in bed every 24 hours) for 5 days, before each of two pseudorandomly assigned afternoon assessments following nap-rested or nap-restricted conditions. Actigraphy is applied to monitor sleep, and occipital alpha power is detected from resting-state EEG to objectively measure sleepiness. Empathy (Empathic for Pain Event-related Potential Paradigm) and prosocial behaviors (Concern for Others Behavioral Paradigm) were measured at each assessment. The effects of nap restriction were analyzed with paired t-test/Wilcoxon matched-pairs sign rank test and repeated-measures ANOVA.

Inclusion Criteria:

1. healthy, typically developing, Intelligence quotient (IQ) ≥ 85;
2. never diagnosed with emotional-behavioral problems;
3. sleeping on a regular daily schedule;
4. reported napping three or more times every week, ≤ one nap in one day;
5. able to fall asleep by themselves.

Exclusion Criteria:

1. not able to fall asleep alone;
2. travel beyond two time zones within 3 months of the study;
3. use of medications influencing sleep or alertness;
4. reported or diagnosed sleep problems (such as obstructive sleep apnea (OSA), narcolepsy, parasomnia, insomnia, etc.) ;
5. history of neurodevelopmental diseases, including developmental delay, epilepsy, chronic medical conditions, lead poisoning and head injuries involving loss of consciousness;
6. conceptual age <35 weeks or > 45 weeks;
7. birth weight < 2,500 grams;
8. Children's Behaviors Checklist (CBCL) total score > 70;
9. a first-degree family history of diagnosed narcolepsy, psychosis or bipolar disorder.